Problem(s) Encountered:

Around 2 am, background count was ~8000. I figured out it is because of

high CCD temperature (~ -35). It is weird because I filled liquid nitrogen and 5:30pm and I checked the nitrogen leaking which means it is totally filled.

Anyway, around 3 am, I refilled nitrogen again, temperature went down, and background count came back to normal value.

Solutions:

An improper LN2 fill can ruin your night, and perhaps the next couple nights as well!  It’s always better to waste a little extra LN2 and be sure the detector is full.  The LN2 should be pouring out at a steady flow before stopping the fill.  If there is any question, consult with MDM staff to see a demonstration of a proper fill.